case study #2: peer/ssc tall building design

Tony Ghodsi

Case study #2

PEER/SSC Tall Building Design

Acknowledgments:

Jose Antonio Flores Ruiz Robert Englekirk

Claire Massie Yangbo Chen Erzen Hoda Maria Bravo

Kathy Lee

Location:

•  Downtown Los Angeles, CA.

Story heights:

•  10.5 ft. typical

•  13.6 ft. from ground floor to 2nd

•  11.5 ft. at roof

Use:

•  42 Story Hotel / residential with 4 parking levels below ground

Building Description

Slab Construction:

•  10 in. thick at parking

•  12 in. thick at ground floor

•  8 in. thick post-tensioned typical

•  10 in. thick at roof

Seismic Weight:

•  102,000 kips (Above ground floor)

Building Description

Building 2

Building 2A Building 2B

Code design

IBC 2006

ASCE 7-05 ACI 318-08

LATBSDC 2008

Service Level Collapse Prevention

25 years return period

2,475 years return period

Design Program

Stiffness Modifiers

Stiffness Modifiers

Stiffness Modifiers

Typical Plan View at Ground Floor and Below

Typical Plan View at 2nd Floor and Above

Code Design Building 2A

Building 2A Shear Wall properties Shear wall thickness and

concrete strength

t = 18”

f’c = 5,000 psi

t = 24”

f’c = 6,000 psi

20th

Frame Beam Properties

30” x 36”

f’c = 5000 psi

Frame column concrete strength

f’c = 6,000 psi

f’c = 5,000 psi

15th

10th

Ground

f’c = 8,000 psi

f’c = 10,000 psi

Frames A & F

Interior & Corner columns

36” x 36”

Building 2A Frame Properties

Frame column concrete strength

f’c = 5,000 psi

f’c = 6,000 psi

15th

10th

Ground

f’c = 8,000 psi

f’c = 10,000 psi

Frames 2 & 5

Interior columns at gridline B & E

42” x 42” from Ground to 25th

36” x 36” from 25th to Roof

Interior columns at gridline C.5

46” x 46” from Ground to 10th

42” x 42” from 10th to 25th

36” x 36” from 25th to Roof

Building 2A Frame Properties

VB = 0.043 W

Design base shear:

T1 = 5.50 sec.

T2 = 4.97 sec.

T3 = 2.98 sec.

Periods: Site specific design response spectra

Building 2A Periods and Base Shear

Vb min = 0.043 W

Period = 5.5 sec

Vb site specific = 0.112 W

Design Ductility

R = 2.6

Building 2A Static Shear Distribution

Maximum inter-story drift allowed

0.020 hn

Building 2A Inter-story Drifts

Service Level and Collapse Prevention Design Building 2B

1.  Service level check is for an earthquake event of 25 year return period with 2.5% viscous damping.

3.  Up to 20% of the elements with ductile actions are allowed to reach 150% of their capacity under the serviceability check.

5.  The minimum base shear specified by the LATBSDC (2008) is waived.

7.  Strengths for ductile actions at service level are calculated using strength reduction factors per ACI 318-08.

Exceptions from LATBSDC

Performance Design

t = 16”

f’c = 5,000 psi

t = 24”

f’c = 8,000 psi

20th

30th

t = 18”

f’c = 6,000 psi

t = 18”

f’c = 5,000 psi

t = 24”

f’c = 6,000 psi

20th

Code Design Shear Wall Concrete Strength and Thickness Comparison

Corner Column Concrete Strength and Size Comparison Performance Design Code Design

f’c = 6,000 psi

f’c = 5,000 psi

15th

10th

Ground

f’c = 8,000 psi

f’c = 10,000 psi

36” x 36” f’c = 6,000 psi

f’c = 5,000 psi

22nd

18th

3rd

f’c = 8,000 psi

f’c = 10,000 psi

36” x 36”

42” x 42”

30th

10th

46” x 46”

Response Spectrum Analysis for Service Level Earthquake Building 2B

•  Gravity load combinations per IBC 2006

•  Earthquake actions at service level per

DL + 0.25LL ± Eservice

Service Level Acceptance Criteria

T1 = 4.13 sec.

T2 = 3.81 sec.

T3 = 2.21 sec.

Periods:

VBx = 0.043 W

VBy = 0.047 W

Base Shear:

2.5% damped service level site specific response spectra

Building 2B Service Level Periods and Base Shear

Ductile actions:

Expected material properties

φ per code

Brittle actions:

Specified material properties

φ per code

CAUTION:

Specified material properties

φ per code

Could result in the same design as that prescribed

by code

Strength of Elements at Service Level

Classification of Actions

Overall drift allowed at service level

0.005 hn

Inter-story Drifts at Service Level

Modal Analysis Peak Shear at Service Level on X Direction

Pier 1 Service Level Peak Shear on X Direction

150% φVNexpected

20% of elements

Coupling Beam Shear Demand at Service Level

Frames 2 & 5 Beam Moment Demand at Service Level

Positive Moments Negative Moments Positive Moments Negative Moments

Corner Beam-Column Joint Interior Beam-Column Joint

20% of elements

150% φΜNexpected

Step by Step Time-History Non-Linear Analyses at MCE Level Building 2B

Collapse Prevention MCE Level Acceptance Criteria

Collapse Prevention MCE Level Acceptance Criteria

Collapse Prevention MCE Level Acceptance Criteria

Collapse Prevention MCE Level Acceptance Criteria

Collapse Prevention MCE Level Acceptance Criteria

Ductile actions:

Average of 7 records

Brittle actions:

Average of 7 records times 1.5

Expected material properties

φ of 1

Demand Actions at MCE Level

Expected material properties

φ equals 1

Element Capacity at MCE Level

Specified material properties

φ equals 1

Element Properties for Non-Linear Model

T1 = 4.93 sec.

T2 = 4.50 sec.

T3 = 2.78 sec.

Periods:

Base Shear:

VBx = 0.154 W

VBy = 0.190 W

MCE target response spectra

Building 2B MCE Periods and Average Base Shear

MCE Records Adjusted to Match Target Response Spectra

Peak Story Shear at MCE Level

Maximum inter-story drift allowed at MCE

level

0.030 hn

Inter-story Drifts at MCE Level on X direction

Pier 1 MCE Average Shear on X Direction

Maximum compression strain allowed for confined concrete

εu = 0.015 in/in

Maximum compression strain allowed for unconfined concrete

εu = 0.003 in/in

Compression Strain at Corner by Pier 1

Maximum Coupling Beam rotation allowed

θu = 0.06 rad

Coupling Beam Rotation at MCE Level

Corner Column Peak Shear on X Direction at MCE Level

0.4 f’cexp Ag

Corner Column Peak Compression at MCE Level

θu = 0.045 rad

Frame A Peak Beam Rotation at MCE Level

T1 = 5.5 sec.

T2 = 4.97 sec.

T3 = 2.98 sec.

Code design periods

Base Shear:

VBx = 0.043 W

VBy = 0.043 W

T1 = 4.13 sec.

T2 = 3.81 sec.

T3 = 2.21 sec.

VBx = 0.043 W

VBy = 0.047 W

T1 = 4.93 sec.

T2 = 4.50 sec.

T3 = 2.78 sec.

VBx = 0.154 W

VBy = 0.190 W

Service level periods MCE level periods

Period and Base Shear Comparison

Landers Yermo maximum shear on X direction

VBx = 11.1 % VBx = 13.5 %

20 % increase

Lateral Restrain Provided by Soil Below Ground Floor

VBx = 10.7 % VBx = 15.4 %

44 % increase

Loma Prieta Gilroy maximum shear on X direction Lateral Restrain Provided by Soil Below Ground Floor

Compression

178% increase

Code design column at seismic base:

36”x 36” column

f’c = 8,000 psi

Non-linear design column at seismic base:

46”x 46” column

f’c = 10,000 psi

Corner Column Axial Load Comparison

φPn /

(f’c

Ag)

φPn,max = 0.8φ [0.85f ’c(Ag-Ast) + fyAst] Eq. 10-2 ACI 318-08

Code Maximum Axial Load

4#9 T&B

4#9 T&B

29th

8#9 T&B

Code design: Performance design:

Frame Beam Longitudinal Reinforcing Comparison

Code design: Performance design:

4#9

6#10

21st

14th 4#11

4#10

10#11

21st

10th

8#11

6#10

32nd

Coupling Beam Diagonal Reinforcing Comparison

MCE Pseudo-velocity Response Spectra Comparison At 1 second:

Code = 57 in/sec

Site Specific PEER = 47 in/sec

Downtown 1 & 2 70 in/sec

Westwood = 84 in/sec

At 5 seconds:

Code = 57 in/sec

Site Specific PEER = 43 in/sec

Downtown 2 = 50 in/sec

Westwood = 61 in/sec

The Englekirk Companies Questions?